Glacial events and continental weathering evolution of syn-, inter-, and post-glaciation during the middle–late Neoproterozoic period in the southwestern Tarim Craton, China

A better understanding of Neoproterozoic glacial events and continental chemical weathering signals during syn-, inter-, and post-glaciation is crucial to the study of global glaciation. Middle−late Neoproterozoic glacial strata have been identified at the southwestern margin of the Tarim Craton in China, but their sedimentary environment, the evolutionary history of chemical weathering intensity, and how the strata relate to the Neoproterozoic glacial events remain unclear. This study presents new sedimentological, geochronological, and geochemical data to address these concerns. The sedimentology indicates an environmental transition from continental to marine that included two glaciations (i.e., associated with the Bolong and Yutang formations in the southwestern Tarim Craton, China). Based on the maximum depositional age of the interglacial sediments from the Kelixi Formation, which is between 666 Ma and 662 Ma, the Bolong and Yutang glaciations are considered to correspond to the Sturtian and Marinoan glaciations. The glacial features reveal that the Bolong and Yutang formations recorded four glacial cycles and a glacial retreat process, respectively. Thus, a dynamic glacial environment with open ocean conditions prevailed during Cryogenian time. The relatively high corrected chemical index of alteration (CIA_corr) values in otherwise low CIA_corr values documented in the Bolong Formation suggest the existence of warm and humid intervals in the Sturtian glaciation, whereas the low CIA_corr values recorded in the Yutang Formation imply a cold event during the Marinoan glaciation. Also, a three-stage progression of weathering from strong to moderate to fluctuating is suggested by the varying CIA_corr values throughout the Cryogenian interglaciation. Our data also show significantly rising CIA_corr values during the glacial−interglacial transitions, which suggests intensive chemical weathering following the Sturtian and Marinoan deglaciations.